1. Field of the Invention
The present invention relates to gas bolt heaters and, more particularly, to gas bolt heaters which are intended for use in tightening and loosening studs and bolts.
2. Description of the Related Art
The tightening of large studs and bolts in machinery, for example in turbines, heat exchangers, compressors and pumps, is often extremely difficult and time-consuming since such bolts and studs are subjected to high temperatures in use and, therefore, must be heated to expand them to enable them to be sufficiently tightened during assembly of the machinery or to be loosened during disassembly of the machinery. Since the machinery is required to be periodically disassembled for maintenance and for routine inspection for insurance purposes, and since it is necessary to remove the studs and bolts for this purpose, it is highly desirable to be able to heat them so as to cause them to be longitudinally extended to facilitate loosening of them.
It has, therefore, previously been proposed to provide bolt heaters for heating the studs and bolts. Prior art bolt heaters include electric heaters, which are slow in operation, and gas bolt heaters.
Prior art gas bolt heaters employ an oxy-acetylene torch to provide a flow of hot gases through a hollow core of a stud or a bolt.
However, it has been found, in practice, that it is a substantial disadvantage of such prior art gas bolt heaters that the flame from the tip of the oxy-acetylene torch can impinge on and damage the heater.
According to the present invention, there is provided a gas bolt heater having a hollow cylindrical housing defining a cylindrical chamber within the housing, a heating tube projecting from one end of the housing and having a longitudinal bore extending through the heating tube, a first cylindrical insert closing the lower end of the chamber and located in one end of the housing, the first cylindrical insert having a through opening communicating with the bore of the heating tube, and a second cylindrical insert located within an opposite end of the cylindrical housing at an upper end of the chamber, the second cylindrical insert having an elongate passage extending axially of the cylindrical housing through the second cylindrical insert. A plurality of downwardly convergent air passages in the second cylindrical insert have mouths distributed around the elongate passage, at a lower end of the passage, and an air supply duct communicates through the cylindrical housing with the air outlet passages.
When the gas bolt heater according to the present invention is in use, air jets discharge from the mouths of the air outlet passages around an outlet end of a tip of an oxy-acetylene torch inserted through the elongate passage. In this way, the flame of the oxy-acetylene torch is directed longitudinally of the cylindrical chamber, so that the flame does not impinge directly on the wall of housing. The useful life of the gas bolt heater is thereby substantially extended.
In a preferred embodiment of the invention, the elongate passage is dimensioned to snugly receive therethrough the tip of the oxy-acetylene torch and has a length sufficient to hold the tip so that the tip is co-axial with the cylindrical chamber. In this way, the oxy-acetylene torch tip is held so that the flame of the torch extends along the axis of the cylindrical chamber, thus further counter-acting damage to the wall of the chamber by the flame.
Also, the through opening of the first cylindrical insert, in the preferred embodiment of the invention, includes an outwardly open, downwardly convergently tapered mouth, which may be frusto-conical in shape, and which facilitates flow of the hot gases from the chamber through the elongate passage and into the heating tube with reduced turbulence.
It has been found to be highly advantageous to provide a cooling air supply for cooling the torch tip, since such cooling substantially increases the useful life of the torch tip. Accordingly, a cooling air duct is connected to an upper end of the housing, which is provided with an air outlet communicating with the cooling air supply duct, and the air outlet is directed to discharge cooling air onto the torch tip.